ANDROID SQlite not synchronize

This is button update in main

btnUpdate.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Log.e(TAG,"ButtonUpdate clicked"); new UpdateDB(MainActivity.this); txtLastUpdateShow.setText(db.getLastUpdateTime()); } });

This is updatedb class:

  public UpdateDB(Activity activity){
    Log.e(TAG,"UpdateDB constructor");
    this.mActivity = activity;

    Log.e(TAG,"ButtonUpdate clicked");
    // events = new ArrayList();
    eventRetriever = new EventRetriever(mActivity);
    eventRetriever.execute();
    Log.e(TAG,"UpdateDB constructor async executed");
    Log.e(TAG,"UpdateDB constructor async executed");
    currentDate = Calendar.getInstance(); //Get the current date
    db = new DBHandler(mActivity);

    db.setLastUpdateTime();
    db.deleteOldEvents();
    Log.e(TAG,"DB updated");
    Log.e(TAG,"DB updated");

    Log.e(TAG,"DB deleteoldevents called,end of update db");

}

after asycntask executed here, it goes to website and download information. It takes up to 10 minutes sometimes.

Sometimes as soon as i hit button, the textview of lastupdated becomes today's date but sometimes it becomes at the end of asynctask.

Now methods in dbhelper class:

This is constructr:

    public DBHandler(Context context) {//, Activity mActivity
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
    Log.e(TAG,"db handler construct");

   }
}


 public void deleteOldEvents(){
    Log.e(TAG,"db handler deleteOldEvents");
    Log.e(    "Chico","db handler deleteOldEvents");
    currentDate = Calendar.getInstance();
    formatter= new SimpleDateFormat("yyyy-MM-dd HH:mm");//for sqlite
    String sql = "DELETE FROM "+TABLE_EVENTS+" WHERE "+KEY_END_TIME+" < ('"
            + formatter.format(currentDate.getTime())+"')"
            +" OR "+KEY_END_TIME+" < ('"
           + formatter.format(currentDate.getTime()).substring(0,10)+"')";



    db = this.getWritableDatabase();
    Cursor cursor = db.rawQuery(sql, null);
    if (cursor.moveToFirst()) {
        do {
            Event event = new Event();
            // will be deleted here


        } while (cursor.moveToNext());
    }

    Log.e(TAG,"db handler delete events end");

}



 public String getLastUpdateTime(){
    Log.e(TAG,"db handler getLastUpdateTime()");

    db = this.getWritableDatabase();
    String query = "SELECT "+KEY_START_TIME+" from "+TABLE_EVENTS+" WHERE "+KEY_LINK+" = 'LastUpdate'";
    Cursor c = db.rawQuery(query,null);

    if (c != null && c.moveToFirst()) {
        lastUpdateTime = c.getString(0);
        Log.e("Chico","db handler getLastUpdateTime() lstupdate:+ "+lastUpdateTime+" "+c.getString(0));
    }

    return lastUpdateTime;
}




  public void setLastUpdateTime() {

        Log.e(TAG,"db handler setLastUpdateTime: ");
        SQLiteDatabase db = this.getWritableDatabase();
        formatter= new SimpleDateFormat("yyyy-MM-dd");

        currentDate = Calendar.getInstance();
        ContentValues values = new ContentValues();

        values.put(KEY_START_TIME, formatter.format(currentDate.getTime())); // Event start
        values.put(KEY_END_TIME, formatter.format(currentDate.getTime()));
db.insertWithOnConflict(TABLE_EVENTS,null,values,SQLiteDatabase.CONFLICT_REPLACE);

        Log.e(TAG","db handler setLastUpdateTime: "+formatter.format(currentDate.getTime()));


        db.update(TABLE_EVENTS, values, KEY_LINK +"="+ "'LastUpdate'", null);
        db.close(); // Closing database connection
    }

But log output says this after i hit update button:

    ButtonUpdate clicked

UpdateDB constructor EventRetriever constructor onPreExecute() UpdateDB constructor async executed

 doinbackground
 db handler construct
db handler construct
 db handler setLastUpdateTime: 
 doitbackground university itu
 connect itu

 db handler deleteOldEvents

db handler delete events sonu
DB updated

 db handler getLastUpdateTime()

I stopped here the program.

This last log says, the buttınupdate at the beginning i wrote, it calls this to write to textview. But it cant find (before this it was also null.) Why cant it find? I set a lastupdate row in database in

setlastupdate()

Should i use a method to check if update successful? But this is not problem for now because even if it is not successful, it should write to main textview. Maybe i must use an intent to go back to main?

Only a dialog comes inprexecute and postexecute gone. SO, in still view of main.

As i told, sometimes it cant update the textview but sometimes not. I tried synchornized but it did not work.

And here, database only was managed by setlastupdate because, onpostexecute i write to databse and it was still in doitbackground. So no need synchronize?